This document discusses the skin's defenses against various physical and chemical agents. It has two layers - the epidermis and dermis - which provide protection. The skin limits water loss, guards against light, heat and cold. Intact skin and secretions provide defense, but this can be impaired. The skin can react to mechanical, physical, biological and chemical factors alone or combined. It discusses various injuries that can occur like burns, miliaria, pigment changes, and cancers due to excessive sunlight exposure. Thermal, electrical and cold injuries are also summarized.